While the technology for cellular communication is constantly evolving, with network providers pushing the 3G/4G technologies into the market, legacy 2G technologies still account for a major portion of total mobile broadband connections, and subsequently cellular handsets have to support 2G, 3G, and 4G modes of communications. Developing such a multi-standard mobile terminal demands a broadband modem chip with the highest possible levels of integration within a minimum silicon area, which can be difficult and costly.
One reason for the difficulty is that the electrical and system requirements specifications of the 2G, 3G, and 4G standards are significantly different. The 2G standard uses a time division multiple access (TDMA) system in which the mobile terminal's transceiver operates in burst mode (i.e., quickly turning on and then off) so it can transmit in its allocated time slot in a subframe of eight slots. See, e.g., European Telecommunications Standards Institute (ETSI) Global System for Mobile Communications (GSM) 05.05 ver. 8.5.1 Release 1999: “Digital cellular telecommunications system (Phase 2+); Radio transmission and reception” (EN 300 910 V8.5.1 (2000-11)) (hereinafter “ETSI GSM Release 1999” will refer collectively to the documents forming ETSI GSM Release 1999); online at http://www.etsi.org/deliver/etsi_en/300900_300999/300910/08.05.01_60/en_300910v080501p.pdf, which is hereby incorporated by reference in its entirety. Other standards, such as 3G and 4G, use, for example, frequency division multiple access (FDMA), orthogonal FDMA (OFDMA), and spatial diversity (such as, e.g., multiple input multiple output (MIMO)), as well as TDMA.
In legacy 2G handsets, a dedicated 2G-PA front-end module with power-ramp control was used to guarantee these conditions and more. However, such a dedicated 2G-PA is too expensive to implement in a multiple standard mobile terminal, e.g., a mobile terminal that has the capability to transmit and receive 2G, 3G, and 4G standard signals.